Why is the destructor called when the object is passed by reference?

Question

I pass an Image object to my hash table with the method insert().

htImages.insert(WALL_UP_CLOSE, imgWalls[WALL_UP_CLOSE]);

As you can see, I'm passing the object into Value by reference.

void insert(const Key &key, const Value &value)
{
    Entry entry;
    int index;

    // Build up entry structure
    entry.m_key = key;
    entry.m_value = value;

    // Build the insertion index
    index = m_hash(key) % m_size;

    // Insert the value
    m_table[index].append(entry);

    m_count++;
}

However, once this function ends at the last line, the destructor below is being called.

Image::~Image()
{
    glDeleteTextures(1, &m_handle);
    refCount--;
}

My preference is that the destructor is not called. I'm passing it by reference, so why is the destructor being called?

**How** are you passing it? Show us the code. All the relevant code, in fact. — Konrad Rudolph, Jan 17 '15 at 21:33
Show the definition of `Entry`, the type of `m_table`, and the code calling this function. — Ben Voigt, Jan 17 '15 at 21:34
You are creating `Key` and `Value` subobjects together with `entry` — Columbo, Jan 17 '15 at 21:34
Hmm, that's one out of the three things I listed that we need to see. — Ben Voigt, Jan 17 '15 at 21:37

score 3 · Accepted Answer · answered Jan 17 '15 at 21:35

3

You have a local variable of type Entry, which is automatically destroyed at the end of the function.

When it is destroyed, destructors run for each of its subobjects.

Probably entry.m_value = value; is copying something, and the extra copy needs to be cleaned up.

answered Jan 17 '15 at 21:35

Ben Voigt

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Thanks for spotting this simple issue out. Giving Entry a static modifier solved the issue. – Phil Jan 17 '15 at 21:51
@Phil: I somehow doubt that really fixes it. As I already said, `entry.m_value = value;` looks like a copy assignment operator. Where does that copy go? – Ben Voigt Jan 17 '15 at 21:52

Why is the destructor called when the object is passed by reference?

1 Answers1

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